Thermal Imaging: Let’s Talk Thermal Imaging


When we talk about thermal imaging, certain topics can become confusing or misunderstood. Let’s try to uncomplicate some of these topics. Unfortunately, this article will only scratch the surface of each topic.
Topic #1: Temperature Sensing Is Accurate

Don’t believe this. You should confront this falsity at every opportunity. The right way to phrase this is, “Temperature sensing is sometimes accurate enough to be relevant to decision making.” What’s the difference, you ask? Well, even under controlled laboratory conditions, radiometry (temperature sensing) is only marginally accurate—often to a plus or minus 10 percent. But when temperature sensing is inaccurate, it is often wildly inaccurate. This is not a statement about the quality of the thermal imager (TI). The primary causes of inaccuracies are well beyond the control of the manufacturer, but you could roll them all under one umbrella called “real life.” Real life is not a lab. Real life is full of smoke, extreme heat, shiny surfaces, superheated gases, condensation, and the like, all of which contribute to inaccuracies. Temperature sensing is not valueless; rather, it must be taken in context. Please remember that it can be wildly inaccurate, even under rather mundane, real-life circumstances.

Understanding the limitations of a TI will help you better navigate through a structure safely.

1 Understanding the limitations of a TI will help you better navigate through a structure safely. (Photo courtesy of Bullard.)

Topic #2: Image Freezing

Every fire service TI sold today uses microbolometer technology, but many of the older barium strontium titanate (BST) TIs are still in use. Don’t confuse yourself with what each means (see Topic #4 below), but suffice it to say that these two technologies make up 99 percent of all TIs used in the fire service today and behave very differently. Both technologies must periodically calibrate their respective thermal sensors; however, microbolometers use an internal shutter to do so, and a BST does not. Microbolometers offer a multitude of advantages over BST in terms of size, power consumption, durability, dynamic range, electronics integration, and others, but one drawback is the use of a shutter for calibration. When the shutter closes, known as Non-Uniformity Correction (NUC), all incoming heat is blocked and the TI is blind for a split second. While the TI is blind, the image seen immediately before the NUC is frozen on the display. There is nothing you as a firefighter can do to make this stop, but TIs with greater refresh rates of 30 Hz allow for not missing any important details.

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NUC occurs at two times:

  1. Whenever the TI changes gain states from high sense to low sense or from low sense to high sense. When the TI is exposed to very high heat sources, it must turn its internal gain state down, to what is known as low sense; however, when viewing less-intense heat sources, the TI must turn its internal gain up, to what is known as high sense. This allows for consistency of picture quality but requires calibration and a NUC.
  2. Whenever the TI itself thinks it needs to. Left alone in a room, staring at a mundane, ambient scene, the TI will perform a NUC at fairly regular intervals, which differ by manufacturer but routinely are in the range of every two to four minutes. When exposed to more dynamic scenes, the TI will experience NUC more often.

Although inconvenient at times, NUC is necessary to make sure the image is of high quality and accurate in what it displays.

Topic #3: Image Quality Is Everything

Image quality is not everything. Image quality is one thing. Having and using a TI are everything. Each department must make its own decisions about what is most important. Image quality is important as is durability, size, battery life, and other considerations. No feature is universal, and no feature will satisfy everyone.

TIs are a major expense for many departments, and most fear buyer’s remorse after the purchase. Most departments want to buy the very best TI that they can afford, but I have seen many departments bypass the opportunity to buy a TI because they could not afford the best image quality. Any TI is better than no TI. Image quality is often the primary cost driver in a TI, and it is overrated. If you can afford better image quality, then by all means buy it. Every TI manufactured for and sold to the fire service has sufficient image quality for navigating a structure, locating victims, and identifying secondary means of egress. I don’t care if you go to eBay to buy a TI that is 10 years old if that is all you can afford, because even the image quality of a 10-year-old TI is better than no TI at all.

Topic #4: Thermal Imaging Is Complicated

TIs are technical and complicated. Thermal imaging is neither. One of the best things about a TI is that it is extremely intuitive for the most common tasks such as navigation, victim location, and egress. TIs should never replace basic firefighting skills, but don’t get caught up in the technology trap. If you are interested in how a TI works, then seek the knowledge, but don’t fall victim to the belief that thermal imaging requires extensive, advanced training to use. You should always take advantage of training if you can find it; using a TI is not complicated, but you do have to know how to use it!

Topic #5: “I Don’t Need a TI”

Of course, you don’t. Twenty years ago, long coats and high boots were sufficient, and you did not need full turnouts. Thirty years ago, breathing black soot and vomiting were sufficient, and you did not need a self-contained breathing apparatus either.

You don’t need a TI. You can definitely fight fire without one. The question is: “Should you?” Why would you not take advantage of the ability to see in an otherwise pitch-black environment? Why would you bypass the opportunity to locate a victim faster? Better yet, why would you bypass the opportunity to find one of your own faster? If you were the one trapped and calling a Mayday, would you want your rapid intervention team using a TI? I would. Is it necessary to use a TI to rescue a down firefighter? No. Is it preferable? Unequivocally, yes.

Covering these topics only scratches the surface. Of course, there is more to talk about on each one—as the technology and use of TIs mature, so, too, must the understanding. As with anything, strive for common sense and sound judgment. If you don’t understand something, seek answers. In the face of a claim that does not pass the drop test, ask for proof. Challenge everything. Confusion and misunderstanding can lead to disastrous results.

Manfred Kihn is a 19-year veteran of the fire service, having served as an ambulance officer, emergency services specialist, firefighter, captain, and fire chief. He has been a member of Bullard’s Emergency Responder team since 2005 and is the company’s fire training specialist for thermal imaging technology. He is certified through the Law Enforcement Thermographers’ Association (LETA) as a thermal imaging instructor and is a recipient of the Ontario Medal for Firefighters Bravery. If you have questions about thermal imaging, you can e-mail him at

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